Three-dimensional atrial wall thickness maps to inform catheter ablation procedures for atrial fibrillation

Abstract

Aims: Transmural lesion formation is critical to success in atrial fibrillation ablation and is dependent on left atrial wall thickness (LAWT). Pre- and peri-procedural planning may benefit from LAWT measurements.

Methods and results: To calculate the LAWT, the Laplace equation was solved over a finite element mesh of the left atrium derived from the segmented computed tomographic angiography (CTA) dataset. Local LAWT was then calculated from the length of field lines derived from the Laplace solution that spanned the wall from the endocardium or epicardium. The method was validated on an atrium phantom and retrospectively applied to 10 patients who underwent routine coronary CTA for standard clinical indications at our institute. The Laplace wall thickness algorithm was validated on the left atrium phantom. Wall thickness measurements had errors of <0.2 mm for thicknesses of 0.5-5.0 mm that are attributed to image resolution and segmentation artefacts. Left atrial wall thickness measurements were performed on 10 patients. Successful comprehensive LAWT maps were generated in all patients from the coronary CTA images. Mean LAWT measurements ranged from 0.6 to 1.0 mm and showed significant inter and intra patient variability.

Conclusions: Left atrial wall thickness can be measured robustly and efficiently across the whole left atrium using a solution of the Laplace equation over a finite element mesh of the left atrium. Further studies are indicated to determine whether the integration of LAWT maps into pre-existing 3D anatomical mapping systems may provide important anatomical information for guiding radiofrequency ablation.

Keywords: Ablation; Atrial fibrillation; Cardiac computed tomography; Finite element modelling; Left atrial wall thickness; Mapping.

Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.

Figures

Figure 1

Schematic depiction of image processing pipeline and approximate timings for calculating the LAWT from CTA images.

Figure 2

Schematic showing different approaches for measuring atrial wall thickness between the endocardium (turquoise surface) and epicardium (green surface). (A) Left atrial wall thickness calculated using a normal projection from the surface generates a spurious result at point × (red arrow). (B) Left atrial wall thickness calculated using a nearest point on the opposing surface generates a spurious result for point y. (C) The Laplace method calculates smooth dashed lines between the endocardium and epicardium. Paths that are orthogonal to these lines (black arrows) are used to calculate the wall thickness removing the spurious results observed in the normal projection and nearest point approaches.

Figure 3

Validation of Laplace wall thickness method. (A) Schematic of computed model of the left atrium phantom. (B) Three-dimensional printed and CT images from the atrium phantom. (C) Wall thickness calculated from the computer model of the atrium phantom. (D) Wall thickness calculated from the CT image of the 3D printed atrium phantom. (E) Comparison of the error in each wall segment against the known true value for the computer modelled atrium (top row) and the CT image of the 3D printed phantom (bottom row).

Figure 4

Segmentation of the atrium. (A) Raw CT image. (B) Final segmentation. (C) Cropped image. (D) Application of median filter. (E) Thresholded blood pool. (F) Manually corrected blood pool. (G) Thresholded viable atrial tissue. (H) Right atrium and left ventricle regions. (I) removal of right atrium and left ventricle regions from viable atrial tissue. (J) Removal of blood pool from viable atrial tissue. (K) Dilation of blood pool. (L) Removal of blood pool to identify single voxel shell. (M) Dilation of atrial wall that overlaps with viable atrial tissue. (N) Smoothed atrial wall.

Figure 5

Atria (A) segmentation and corresponding (B) mesh. Increasing zoom of mesh resolution is shown in (C)–(E).

Figure 6

Endocardial and epicardial wall thickness from 0 mm (dark blue) to 5 mm (red) for patients 1–10 (A–J), respectively.

Figure 7

Distribution of wall thickness measurements across endocardium and epicardium surfaces.